Clinical techniques for assessing corneal disease have largely been limited to biomicroscopic examination and morphometric analysis of the cornea. Observations and measurements derived from these two procedures do not necessarily reflect the physiological status of the cornea, and therefore they may not provide sufficient clinical information to predict the effects of disease, surgery, or medical intervention on corneal function. We have recently reported on a clinical test which assesses corneal function by monitoring recovery following induced stromal hydration. Based on corneal thickness recovery profiles following increased hydration levels, a model has been derived that can by used to describe several aspects of corneal hydration control including the percent corneal thickness recovery per hour (PRPH), open-eye steady-state (OESS) thickness, and recovery time to return to OESS thickness. The aims of this proposed project are (1) to investigate the relationship between age and corneal hydration control, (2) to monitor the longitudinal changes in hydration control in normal subjects and in patients with endothelial disease over a 3-year period, and (3) to determine changes in corneal hydration control by making test before and after cataract surgery in eyes with both normal and diseased endothelia. From these studies, we will also investigate the relationship between corneal hydration control and clinical measurements derived from slit lamp examinations and morphometric analysis. We will also further refine the hydration control test procedure and analysis strategies for improved clinical applicability. The long-term goals are to provide the ophthalmologist with an valid and reliable procedure that will (1) assist in determining which patients might require a combined surgery (e.g., penetrating keratoplasty and cataract extraction) as opposed to only a cataract extraction, (2) identify patients at high risk for corneal decompensation, and (3) make it possible to monitor changes in endothelial function that may accompany trauma, corneal disease, inflammation, surgery, or other medial intervention.